During pump operation there is a deep rumble noise emminating from the general area in the old airing cupboard on the first floor. It's very difficult to locate a specific position where the noise is. In the loft, I wouldn't say the boiler itself makes a lot more than expected noise and vibration levels (when you place your hand on the case). The noise reduced somewhat, when I opened up the radiator valves fully (not the thermo valves, the other end). The plumber had set most only slightly open.
Could this imply the bypass valve hasn't been set correctly? How do you set this?
Is this noise unusual or just bad luck with the pipework?
It's really begining to get on my nerves as I've tuned in to it.